The kinetics of the methanolysis of reactions of ethylchloroformate and phenykrhlorafoanate were studied in eight organic solvents covering a wide range of dielectric constant. The methano-lysis rates were followed by conductance measurements. The analysis of the medium effects by multiparameter approaches indicated that polarity, polarizability and electrophilicity of the solvents are responsible for the observed reactivity. The activation enthalpies ΔH ≠ and entropies, of the methanolysis reactions were also discussed in terms of solvent properties.